A HDD is a data storage device used for storing and retrieving digital information using rapidly rotating discs coated with magnetic material. A typical HDD includes one or more rigid rapidly rotating disks with magnetic heads arranged on a moving actuator arm to read and write data onto the disk surfaces. The disks are placed about a spindle, and are spun rapidly about the spindle as information is written to and read from the disk surface as it rotates past the magnetic read-and-write heads that operate closely over the magnetic surface. The read-and-write head is used to detect and modify the magnetization of the material immediately under it. A spindle motor is provided with the spindle for the spinning or rotating of the disks.
The spindle motor used in HDDs is typically a brushless direct current (BLDC) motor, which is an electronically self-commutated motor. The BLDC motor is a 3-phase synchronous motor with a surface mounted permanent magnet ring on the motor that generates sinusoidal back electro-motive force (BEMF) in the stator windings. In electrical machines, such as a motor, where a rotor rotates about a stator in converting electrical energy to or from mechanical energy, position sensors, such as a position encoder may be provided in order to determine the present position of the rotor during operation.
Due to cost, reliability, as well as space issues in the push to miniaturize hardware, some HDD manufacturers presently have chosen to move on from the use of such sensors, and have instead decided to rely on sensorless operation of the spindle motor. In the present art, multiple operation schemes have been proposed for sensorless control in detecting the rotor position, mostly relying on detection and analysis of the resultant BEMF which is generated by an electromagnetic field against the inducing current.
However, in the situation where the spindle motor is at rest, an initial position of the rotor has to be determined in order to correctly start the motor, such that the rotor can be controlled to spin in the correct direction, as well as to determine the sufficient amount of induced electromagnetic torque to rapidly accelerate the rotor of the motor for efficient operation. In such case, the use of BEMF detection is severely restricted, as BEMF generated is at zero, or at very low levels when the rotor is static or almost static.
Hence, a need exists for a system and method for controlling a motor, including determining the initial position of a rotor of a spindle motor, in order to start the motor up quickly and efficiently.